Inductive ignition device

ABSTRACT

An inductive ignition device for spark plugs of an internal combustion engine is having at least one activation circuit for at least one ignition coil and having at least one spark plug. A high-voltage switch associated with the at least one spark plug is brought by a first activation signal of the activation circuit into a conductive, switched-on state. In the switched-on state, the high-voltage switch has passing through it the spark current (I 2 ) of the at least one spark plug (3; 3a to 3n), and which is designed so that without further activation it remains in the conductive state until the spark current falls below a certain value (holding current).

FIELD OF THE INVENTION

The present invention relates to an inductive ignition device for sparkplugs of an internal combustion engine, and also to a method foractivating a spark plug of an internal combustion engine.

BACKGROUND INFORMATION

Inductive ignition devices of the type discussed here are known. Theycan have single spark coils or can be equipped with an electronichigh-voltage distributor. Methods of the aforesaid type are also known.When an internal combustion engine is operating at high speeds, it isoften problematic to perform an ionization current measurement. Thismeasurement is the basis on which the combustion characteristics of theinternal combustion engine can be monitored. It has also been found thatin this operating state, the energy provided for a discharge operationcannot be completely dissipated via a spark plug, but rather thatresidual energy is present after completion of the ignition operation,which can cause the power dissipation in the ignition device to risesharply. Attempts have already been made to provide a current limiter inthe ignition output stage of the ignition device, or to implement acurrent limiter by way of primary resistors. In both cases, however, theresult is high power dissipation in the ignition output stage or in theignition coil. Attempts have also been made to decrease the ignitioncoil energy by reducing the dwell time at high engine speeds. Theproblem which has occurred here, however, is that sufficientavailability of voltage and energy cannot be guaranteed under alloperating conditions.

SUMMARY OF THE INVENTION

The inductive ignition device and method according to the presentinvention eliminate the disadvantages mentioned above. Provision is madefor an ionization current measurement to be made with no need todecrease the available voltage or the secondary initial current that isconveyed to the spark plug. In addition, a "residual energy mode" isavoided in multiple-cylinder engines, even at high engine speeds andeven when activation is provided with only one output stage. In thecontext, at a given energy the spark plugs can be activated with a lowinitial current, resulting in low spark plug wear.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a first exemplary embodiment of an inductive ignitiondevice, having a single spark coil for each spark plug according to thepresent invention.

FIG. 2 shows a first exemplary embodiment of an inductive ignitiondevice having an electronic high-voltage distributor according to thepresent invention.

FIG. 3 shows a second exemplary embodiment of an inductive ignitiondevice having an electronic high-voltage distributor according to thepresent invention.

FIG. 4 shows a schematic diagram of typical voltages and currents thatcan be measured within the inductive ignition devices as shown in FIGS.1 to 3.

DETAILED DESCRIPTION

FIG. 1 shows a schematic circuit diagram of an inductive ignition device1 in which there is associated with each spark plug 3 of an internalcombustion engine, an ignition coil 5 (also referred to as a singlespark coil) that can be activated via an ignition output stage, of whichonly the activation signal 7 over time, which is sent to a switchingdevice (in this case a transistor 9), is indicated here.

Provided on the primary side of ignition coil 5 is a primary winding 11'which is connected on the one hand to a voltage source (labeled with aplus sign) and on the other hand via transistor 9 to ground. Provided onthe secondary side of ignition coil 5, at its high-voltage output 11, isa high-voltage switch 13 which is arranged in connecting path 15 betweenhigh-voltage output 11 and spark plug 3. Winding 17 of the secondaryside of ignition coil 5, connected to high-voltage output 11, is on theother hand grounded via a measurement circuit 19. Measurement circuit 19comprises a Zener diode 21 connected at its cathode to a connectionpoint 23 and at its anode to ground. Connected between connection point23 and ground, parallel to Zener diode 21, is a series circuit made upof a capacitor 25 and a diode 27, the cathode of which is connected toground and the anode of which is connected to capacitor 25. Connectedrespectively to the anode of diode 27 and to capacitor 25 is a resistor29 which is additionally connected to ground. Resistor 29 is thusparallel to diode 27. At the connecting point between diode 27 andcapacitor 25, to which resistor 29 is also connected, there results ameasurement voltage output 31 at which a voltage proportional to theionization current can be measured.

An ignition coil 5, and preferably also a measurement circuit 19, areprovided for each spark plug 3.

The core of inductive ignition device 1 is high-voltage switch 13, whichis provided on the secondary side of ignition coil 5 and is configuredhere as a high-voltage flip-flop diode, of which the cathode isconnected to high-voltage output 11, and the anode to spark plug 3. Adiode 33 of opposite polarization, located parallel to the high-voltageswitch and drawn with dashed lines, indicates that high-voltage switch13 is configured to conduct in the reverse direction. When thehigh-voltage switch 13 is switched off, diode 33 also allows a positivepotential to pass from high-voltage output 11 and via connecting path 15to spark gap 35 of spark plug 3. The positive potential U is applied viacapacitor 25 to spark gap 35 so that an ionization current I_(ION) canbe measured in known fashion. This ionization current providesinformation about the combustion process, in particular about knockingof the cylinder associated with spark plug 3, and about the combustionoccurring the combustion chamber.

The current flowing on the primary side of ignition coil 5 throughtransistor 9 is designated I₁ ; the current flowing on the secondaryside is designated I₂. The activation signal applied to the base oftransistor 9, which derives from an output stage activation system (notdepicted here), is designated U_(ES). A lightning-bolt symbol indicatesthe moment of ignition.

Inductive ignition device 1', which is depicted in FIG. 2, hasfundamentally the same components as the ignition device in FIG. 1.Identical parts have been given the same reference characters.

In inductive ignition device I' as shown in FIG. 2, an activation signal7 of an output stage activation system (not depicted here) is applied toa switch (here indicated once again as transistor 9) which activates asingle ignition coil 5 to which the multiple spark plugs 3a to 3n,arranged in parallel, can be connected. Spark plugs 3a to 3n areconnected, each via a high-voltage switch 13a to 13n, via a connectingpath 15 between high voltage output 11 on the secondary side of ignitioncoil 5 and ground. A separate high-voltage switch is associated witheach spark plug. Diodes 33a to 33n arranged parallel to high-voltageswitches 13a to 13n, drawn with dashed lines, indicate that thehigh-voltage switches 13a to 13n are configured to conduct in thereverse direction.

The energy of ignition coil 5 is distributed (electronically) to sparkplugs 3a to 3n by means of corresponding activation of the high-voltageswitches. FIG. 2 thus shows an ignition device having an electronichigh-voltage distributor.

A measurement circuit 19 identical in configuration to the one depictedand explained with references to FIG. 1 is once again provided on thesecondary side of ignition coil 5, at the end of winding 17 oppositehigh-voltage output 11. Reference is therefore made to the statements inconnection with FIG. 1.

A current I₁ flows on the primary side of ignition coil 5; a current I₂,which is passed on via high-voltage switches 13a to 13n to therespective spark plugs 3a to 3n, flows on the secondary side. Ignitioncoil 5 is once again activated via an activation signal 7, labeledU_(ES), of an output stage activation system (not depicted here) that isapplied to the base of transistor 9. A lightning-bolt symbol once againindicates the moment of ignition.

High-voltage switch 13a to 13n is here, purely by way of example,configured as a light-triggered flip-flop diode which comprises anoverhead-switched high-voltage diode 13'a to 13'n and a light-controlledswitch 13"a to 13"n. The light-controlled switch can be controlled via alight signal that is generated by a suitable light emission element, forexample a light-emitting diode. The light required to triggerconductivity is indicated by two wavy arrows. The current necessary forgeneration of the light is labeled I_(EHV).

Inside the high-voltage switch (e.g. 13a), the two diodes--i.e. thelight controlled switch 13"a and the overhead-switched switch 13'a--areconnected in series, the anode of overhead-switched switch 13'a/13'nbeing connected to spark plug 3a/3n, and its cathode to the anode oflight-controlled switch 13"a/13"n. The cathodes of the light-controlledswitches are connected via connecting path 15 to high-voltage output 11of ignition coil 5. FIG. 2 indicates that spark plugs 3a to 3n areactivated with a negative potential. Light-triggered flip-flop diodes13a to 13n are, as mentioned above, configured to conduct in the reversedirection, i.e. they are conductive at a certain positive measuredpotential (the charge of capacitor 25), so that the ionization currentI_(ION) present across the spark gap of spark plugs 3a to 3n can besensed. The measurement voltage used for the ionization currentmeasurement is 100 V to 500 V, preferably 200 V to 300 V. This appliesto all the circuit variants.

FIG. 3 shows an alternative embodiment of inductive ignition device 1'with an electronic high-voltage distributor depicted in FIG. 2. Ignitiondevice 1" in FIG. 3 differs exclusively in that spark plugs 3a to 3n areactivated with a positive potential, which is applied to spark plugs 3ato 3n via high-voltage output 11 and connecting path 15, and viahigh-voltage switches 13a to 13n. High-voltage switches 13a to 13n areonce again configured as light-triggered flip-flop diodes, and each havea light-controlled switch 13"a to 13'n and a high-voltage flip-flopdiode which represents an overhead-switched switch 13'a to 13'n.Switches 13a to 13n used in the circuit depicted in FIG. 3 arenonconductive in the reverse direction.

The polarization of the diodes of high-voltage switches 13a to 13n isthe reverse of the exemplifying embodiment depicted in FIG. 2. Theanodes of light-controlled switches 13"a to 13"n are thus connected viaconnecting path 15 to high-voltage output 11, while the cathodes ofoverhead-switching switches 13'a to 13'n are connected to spark plugs 3ato 3n.

Measurement circuit 19', however, differs from the one depicted in FIG.1 and 2: it comprises, for example, a series circuit made up of aresistor 37, a diode 39, and a resistor 41. Resistor 37 is connected tothe primary side of ignition coil 5, specifically in this case to thecollector of transistor 9. Connected to the other side of resistor 37 isthe anode of diode 39, the cathode of which is connected to resistor 41and capacitor 42. The end of capacitor 42 opposite resistor 41, at whichthe voltage proportional to ionization current I_(ION) is picked off, isconnected via resistor 44 to ground. At the end of resistor 41 oppositecapacitor 42 there is a connection point 23 to which high-voltageswitches associated with spark plugs 3a to 3n (in this case high-voltagediodes 43a to 43n) are connected; their anodes are connected toconnection point 23, and their cathodes to the end of the spark gap ofspark plugs 3a to 3n, to which high-voltage switches 13a to 13n are alsoconnected. The opposite end of the spark gap of spark plugs 3a to 3n isgrounded.

Measurement circuit 19' causes a positive voltage signal to be appliedto spark plugs 3a to 3n in order to sense ionization current I_(ION).The polarization of high-voltage diodes 43a to 43n prevents the highvoltage applied to spark plugs 3a to 3n from reaching measurementcircuit 19'.

Otherwise the components of inductive ignition device 1" as shown inFIG. 3 correspond to those of the variant embodiment depicted in FIG. 2.Identical parts are given identical reference characters, and referenceis made in that context to the description accompanying FIG. 2.

FIG. 4 schematically shows the change in activation voltage U_(ES),applied to the base of transistor 9, over time t; below that the primarycurrent I₁ in ignition coil 5 over time, and also the secondary currentI₂ in ignition coil 5 that is conveyed to the activated spark plugs, andin a fourth partial diagram the secondary voltage U₂, present at thespark plugs, over time t. Lastly, the last and bottommost partialdiagram in FIG. 4 indicates the current I_(EHV) which serves to activatelight-controlled switches 13"a to 13"n discussed in FIGS. 2 and 3, andthus the electronic high-voltage distributor.

It is evident from the depiction in FIG. 4 that activation voltageU_(ES) is present during the "dwell time" up to time t₁, and is switchedoff at the moment of ignition, indicated by a lightning-bolt symbol. Theprimary current I₁ rises linearly until time t₁ and then drops abruptly.Secondary current I₂ remains at zero until time t₁, and at time t₁ risesto its maximum value. At the same time, the peak for ignition voltage U₂occurs at time t₁. The desired spark duration extends from time t₁ totime t₂. It is evident from FIG. 4 that during the period t₁ <=t<=t₂,secondary current I₂ decreases essentially linearly. The high-voltageswitches of the inductive ignition devices in FIGS. 1 to 3 can beselected so that the switches switch off at the current value of I₂present at time t₂, specifically because the current falls below the"holding current" of said high-voltage switches.

The voltage peak of U₂ at time t₁ causes high-voltage switch 13,configured as an overhead-switching high-voltage flip-flop diode, ofinductive ignition device I as shown in FIG. 1 to become conductive, sothat secondary current I₂ flows across spark gap 35 of spark plug 3,igniting the spark. The spark is extinguished as soon as thehigh-voltage switch switches off. This can be accomplished by the factthat the secondary current falls below the holding current value. It isthus possible to ensure, by means of the specific design of thehigh-voltage switches, that the spark duration is limited. The sparkduration can, however, also be limited by the fact that secondarycurrent I₂ is forced to switch off, and the current thus falls below theholding current value of the high-voltage switch. The secondary currentis switched off by the fact that a second activation signal A, which isdepicted in the topmost partial diagram of FIG. 4, causing current I₁ toflow again, is issued via the activation circuit at time t₂. The secondactivation signal is maintained for a period of 10 microseconds to 500microseconds. An activation signal duration of 100 microseconds hasproven particularly successful. During this period t₂ <=t<t₃, thecurrent I₁ rises and then drops back to a value of zero. This forcestermination of the current flow I₂. The current I₂ thus drops, in adefined and forced fashion, to a value which lies below the holdingcurrent of the high-voltage switch. After a time period of approximately50 microseconds that is also referred to as the "recovery time," avoltage can once again be applied in the forward direction to thehigh-voltage switch.

After the activation signal A switches off at time t₃, the secondaryvoltage U₂ rises again briefly and then drops toward zero. A rapid,defined dissipation of the residual energy in the ignition coil takesplace here, so that U₂ no longer exceeds the inhibiting voltage of thehigh-voltage switches. The latter thus remain in their switched-offstate, so that the spark plugs no longer fire.

The voltage and current profiles indicated in FIG. 4 also occur for theignition systems depicted in FIGS. 2 and 3.

High-voltage switches 13a to 13n, configured as light-triggeredflip-flop diodes, are switched on by activation of light-controlledswitches 13"a to 13"n. The light-triggered switches thus, in theactivated state, enable the connection between the overhead-switchingswitches and high-voltage output 11, so that overhead-switching switches13'a to 13'n can be switched on by overvoltage U₂. Theoverhead-switching switches are enabled by means of a current signalI_(EHV) that is applied, immediately before the occurrence of ignitionvoltage U₂ at time t₁, to light-controlled switches 13"a to 13"n ofspark plugs 3a to 3n, to which the energy of ignition coil 5 is to beconveyed. Purely by way of example, it will be assumed that switchingsignal I_(EHV) is applied to one of light-switchable switches 13"a to13"n for 100 microseconds before and after time t₁. It is evident thatdefined termination of the spark duration does not require any furthersignal I_(EHV) to be applied to the light-switching switches.Light-triggerable switches 13a to 13n, and high-voltage flip-flop diodes13'a to 13'n associated with said switches, are switched off exclusivelyby means of the second activation signal A applied at time t₂, which isdepicted in the topmost partial diagram of FIG. 4.

The result of signal U_(ES), in the case of the ignition devicesdepicted in FIGS. 2 and 3 as well, is therefore that primary current I₁rises again at time t₂, so that here again, the secondary current I₂ isforced to terminate and--as is evident from FIG. 4--drops approximately20 mA in 50 microseconds, so that the spark duration is forced toterminate. In the case of the variant embodiments as shown in FIGS. 2and 3 as well, the secondary voltage U₂ will rise again when the secondactivation signal U_(ES) is switched off at time t₃ --but withoutreaching the inhibiting voltage of overhead-switching switches 13'a to13'n--and then decrease toward zero. The residual energy in the sparkplug is thus rapidly dissipated, but without firing the spark plugsagain.

The circuits depicted in FIGS. 1 to 3 are thus characterized by the factthat the spark duration can be deliberately shortened. This is madepossible on the one hand by the use of high-voltage switches--whetherthose depicted in FIG. 1 or those explained with reference to FIGS. 2and 3--whose holding current is selected so that secondary current 12 isswitched on at time t₂ because the current has fallen below the holdingcurrent of the high-voltage switches.

Essentially reliable operation of the circuits results if the secondarycurrent I₂ is deliberately switched off by a second activation signal Athat is generated at time t₂ and sent to the ignition coil. As describedabove, the second activation signal at time t₂ decreases the secondarycurrent I₂ in defined fashion to zero, so that the high-voltage switchesare definitively switched off and remain switched off after a certainperiod (recovery time).

Because the high-voltage switches are switched off, the spark plugs aredecoupled from the ignition coil, so that even when the secondaryvoltage U₂ rises after time t₃, refiring of the plugs is impossible.

These explanations indicate on the one hand the operation of theinductive ignition devices as shown in FIGS. 1 to 3, and on the otherhand the method for activating a spark plug of an internal combustionengine by means of an inductive ignition device which is characterizedprecisely by the fact that in order to implement a defined sparkduration for a spark plug, two activation signals are generated. Thefirst activation signal serves to initiate the ignition operation attime t₁ ; the purpose of the second activation signal A, issued at timet₂, is to switch off the secondary current in the spark plug in definedfashion and thus limit the spark duration. It has been found that thesecond activation signal must be made available for a period of,preferably, 100 microseconds, so that on the one hand the recovery timefor the high-voltage switches being used is observed. On the other hand,the short duration of the second activation signal ensures that when theprimary current I₁ is switched off, the secondary current I₂ does notrise again at time t₃.

Because of the specific embodiment of the circuits of FIGS. 1 to 3, andthe design of the method, a measurement current can be applied to thespark plugs, in which context measurement circuits 19 and 19', whichwere depicted and explained in FIGS. 1-2 and 3, respectively, can beused. The measurement current which flows across the spark gap of thespark plug is analyzed while the ignition spark is no longer active. Itflows because of the ions present in the combustion chamber duringcombustion. With this method, also referred to as ionization currentmeasurement, the combustion process can be monitored. The measurementcurrent lies within a range from 20 microamperes to 200 microamperesPreferably a measurement current of 50 microamperes to 100 microamperesis selected. From the explanations with reference to the high-voltageswitches used in FIGS. 1 and 2, it is clear that reverse-conductingflip-flop diodes, i.e. reverse-conducting high-voltage diodes orreverse-conducting light-triggered flip-flop diodes, are used to performthe ionization current measurement, so that the ionization currentmeasurement can be performed with relatively little effort. If, asexplained with reference to FIG. 1, single spark coils are used, it ispossible to provide a separate measurement circuit for each spark plug.It is also possible to use a single measurement circuit for a pluralityof spark plugs, for example four.

In FIG. 3, high-voltage switches which are nonconductive in the reversedirection are used. The measurement circuit depicted in FIG. 3 is alsousable for arrangements as defined in FIG. 1; high-voltage switches 13as defined in FIG. 1 are then configured to be nonconductive in thereverse direction.

It is evident from the statements above that in the case of theinductive ignition devices shown in FIGS. 1 to 3, ionization currentmeasurement is possible with no need to reduce the available voltagesent to the spark plugs or the secondary initial current I₂. Because thesecondary current is "switched off" in defined fashion, a high energy inthe ignition coil can be sent to the plugs, so that sufficient voltageand energy are available under all operating conditions.

Deliberate switching off of the high-voltage switches, either by meansof a specific definition of the holding current of the high-voltageswitches or, preferably by means of a second activation signal, ensuresthat elevated power dissipation cannot occur in the output stageactivation system or the spark plug.

The fact that the high-voltage switch is made nonconductive means theenergy remaining in the ignition coil can decay with a short timeconstant without allowing refiring of the spark plugs. Lastly,deliberate termination of the spark duration can prevent residual energyoperation in multiple-cylinder engines, for example in engines with morethan five cylinders, at high engine speed and when activation is beingprovided by only one output stage. In this context, for a given energy arelatively low initial current can be selected for the spark plugs,resulting in a correspondingly long spark duration. The low initialvalue of the secondary current I₂ results in relatively little plugwear. This operating mode can be implemented, in particular, inconjunction with an electronic high-voltage distributor, as wasexplained with reference to FIGS. 2 and 3.

What is claimed is:
 1. An inductive ignition device for at least onespark plug of an internal combustion engine, comprising:at least oneactivation circuit for activating at least one ignition coil; and ahigh-voltage switch associated with the at least one spark plug, whereinthe high-voltage switch conducts a spark current of the at least onespark plug when activated into a conductive, switched-on state by afirst activation signal emitted by the at least one activation circuit,the high-voltage switch remaining in the switched-on state until thespark current falls below a holding current value, and wherein the atleast one activation circuit emits a second activation signal forterminating the spark current.
 2. The ignition device according to claim1, wherein the second activation signal generates no further sparkcurrent and causes the high-voltage switch to remain in a switched-offstate after a recovery time.
 3. The ignition device according to claim2, wherein the second activation signal is emitted for a period of timebetween 10 microseconds and 500 microseconds.
 4. The ignition deviceaccording to claim 2, wherein the second activation signal is emittedfor a period of 100 microseconds.
 5. The ignition device according toclaim 1, wherein the high-voltage switch is arranged between ahigh-voltage output on a secondary side of the at least one ignitioncoil and the at least one spark plug.
 6. The ignition device accordingto claim 1, wherein the high-voltage switch includes a flip-flop diodeconfiguration.
 7. The ignition device according to claim 1, wherein thehigh-voltage switch includes a triggerable configuration.
 8. Theignition device according to claim 1, wherein the high-voltage switchincludes a reverse-conducting high-voltage flip-flop diode.
 9. Theignition device according to claim 1, wherein the high-voltage switchincludes a reverse-conducting light-triggered flip-flop diode.
 10. Theignition device according to claim 1, further comprising a measurementcircuit for sensing an ionization current and applying a measurementcurrent to the at least one spark plug.
 11. The ignition deviceaccording to claim 10, wherein the measurement circuit includes:a Zenerdiode, a series arrangement coupled in parallel to the Zener diode andincluding a capacitor arranged in series with respect to a diode, and aresistor coupled in parallel to the diode.
 12. The ignition deviceaccording to claim 10, wherein the measurement circuit includes:a firstseries arrangement coupled to the at least one ignition coil andincluding a first resistor arranged in series with respect to a diode,and a second series arrangement coupled to the first series arrangementand to the high-voltage switch, the second series arrangement includinga second resistor, a capacitor, and a third resistor arranged in serieswith respect to each other.
 13. A method for activating a spark plug ofan internal combustion engine using an inductive ignition device,comprising the steps of:generating a first activation signal serving tocreate an ignition spark; and generating a second activation signal forterminating the ignition spark by switching off a secondary current,thereby defining an ignition spark duration for the spark plug.
 14. Themethod according to claim 13, wherein the second activation signalswitches off a high-speed switch conducting a spark current to the sparkplug.
 15. The method according to claim 13, wherein the secondactivation signal is generated for a period of time between 10microseconds and 500 microseconds.
 16. The method according to claim 13,wherein the second activation signal is generated for a period of 100microseconds.
 17. The method according to claim 13, further comprisingthe steps of:applying a measurement voltage to the spark plug; andmonitoring a combustion process of the internal combustion engine usingan ionization current measurement.
 18. The method according to claim 17,wherein the measurement voltage is in a range of 100 V to 500 V.
 19. Themethod according to claim 17, wherein the measurement voltage is in arange of 200 V to 300 V.